Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 8 - Section 8.4 - Multiplicative Inverses of Matrices and Matrix Equations - Exercise Set - Page 934: 83

Answer

The provided statement is False.

Work Step by Step

The given statement false. The inverse of a $2\times 2$ matrix may not exist. Consider the matrix, $A=\left[ \begin{matrix} a & b \\ c & d \\ \end{matrix} \right]$ Now, compare the matrix to the given matrix. $\begin{align} & a=1 \\ & b=4 \\ & c=2 \\ & d=8 \end{align}$ Now, the inverse is given by, ${{\left[ A \right]}^{-1}}=\frac{1}{ad-bc}\left[ \begin{matrix} d & -b \\ -c & a \\ \end{matrix} \right]$ Substituting the values, we get, $\begin{align} & {{\left[ A \right]}^{-1}}=\frac{1}{ad-bc}\left[ \begin{matrix} d & -b \\ -c & a \\ \end{matrix} \right] \\ & =\frac{1}{\left( 1 \right)\left( 8 \right)-\left( 4 \right)\left( 2 \right)}\left[ \begin{matrix} 8 & -4 \\ -2 & 1 \\ \end{matrix} \right] \\ & =\frac{1}{0}\left[ \begin{matrix} 8 & -4 \\ -2 & 1 \\ \end{matrix} \right] \end{align}$ So, $ad-bc=0$, which shows the matrix is not invertible. Hence, the statement is False.
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